Radio receiving circuit



May 23, 1933. w` VAN B. ROBERTS 1,910,500

RADIO RECEIVING CIRCUIT Filed April 17, 195o w nmmmn INVENTOR WALTER VANRoms ATToNEY 10 ampli cation, together with im Patented May 23, 19Ii3uNiTsD STATES PATENToFi-'ics WALTEBVAN B. ROBERTS, Ol' PRINCETON', mJERSEY, ASSIGNOBVTO RADIO 00B- POBATIO l' AIEBICA, A CORPORATION 0FDELAWARE :same nomme cmUrr Application lied April l?,

My present invention relates to radio receivers, and more` particularlyto a receiving circuit embed ing-a novel type of dire'ct coupled amplier. i

In the receivin circuit art, resistance-coupled audio ampli cation hasalwa s been connected with optimum reproduction quality.

However, due to the lack of electron discharge tubes ssessing. a highenough factor of rfect design in power units, this type o amplificationhas been commercially less acceptable than the more commontransformer-coupledv audio type of amplification. Of late, however, anew type of resistance coupling has made its appearance which differsfrom the accepted type o f resistance cou ling, wherein the usualanodeand control e ectrode resistors are'coupled together by means of acoupling capacity.

As far as the prior art is concerned, this system of direct coupling, orresistance amplification, is welll known. However, the introduction oftubes possessing a high factor of amplification, together with devicesfor procuring very hi h voltages from a wer source have serv .tofacilitate the esign of a direct coupled system of amplicationwhereinthe anode of a preceding tube is directly coupled to the grid ofa succeeding tube with no transformer or condenser between, thusproducing a system capable of both amplification anddetection-amplification. This improved type of direct coupled audioamplification` is capable of varied usage, particularlywhereamplification with a minimum level of distortion is desired.

v Now, I have discovered a method of, and ,devised means for, appl ingthe principles 40 of the direct coupled au io amplifier to produce afairl sensitive receiving circuit of compact an simple construction, thearran ement employed consisting in feeding bac energy from the outputcircuit of the first stage of the direct coupled amplifier to the inputcircuit of the first stage, and in like phase with the energy in thesaid input circuit. i A

Accordingly, it is one ofthe main objects of thepresent invention toprovide a method 1.80., Serial I0. 444,930.

of, and means for, receiving modulated radio frequency signals whichconsists in collecting the signal energy at a desired frequency,detecting the ener impressing the detected energy upon the input circuitof an electron discharge tube directly coupled to the output circuit ofthe detecting tube, and simultaneou'sly feeding back energy from thedetector output circuit to the detector input circuit in regenerativephase with the input energy. 4

Another important object of the present invention is to provide in aradio receiving circuit a direct coupled amplifier consisting of atleast two electron discharge tubes, the c5 anode of one tube beingdirectly connectedyto the control electrode of the succeeding tube, withno transformer or condenser between them, the first tube havingassociated therewith a path for feeding back energ!)7 from the outputthereof to its input circuit in regenerative phase with the energy inthe input circuit. 0

Another object of the invention is to provide an audio amplificationsystem which 15 comprises at least two electron discharge tubes, one ofsaid tubes being a screen grid tube, and the other tube bein a pentodetube,- the anode of the screen grid tube being directly connected to thecontrol electrode of the pentode tube the electrodes of both tubeshaving potential supplied thereto from a common potentiometer connectedacrosspthe power source the screen element circuit of the first tubebeing utilized to regenerate the input circuit of the tube, where theanode circuit of the latter has so .high a resistance in it that thereis not enough anode current to reduce regeneration satisfactorily.

till another important object ofthe invention is to provide'a radioreceiving circuit consisting of a stage of tuned radio frequencyamplification, a tetrode having a tuned input circuit coupled to thefirst stage, and a pentode directly coupled to the output circuit ofthetetrode, and means in series in the screen element circuit of thetetrode for vfeeding back ener from the output circuit of the tetrode toits input circuit, the electrodes of the tetrode and pentode having "10The novel features which ll believe to be characteristic of my inventionare set forth in particularity in the appended claims, the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which ll have indicateddiagrammatically one circuit organization whereby 1 myinvention may becarried into e'ect.

l of the tube 1 is Referring to the accompanying drawing there is showna grounded antenna circuit A, G, coupled, as at M, to the input circuitof an lelectron discharge tube 1, preferably `a tetrode of the screengrid.type,rthe inductance coil 2 in the input circuit being tuned by avariable condenser 3. 'llhe cathode y referably heated from a source ofalternating current (not shown), the screen elementy and anode of thetube 1 receiving potential from sources of positive potential (notshown). The anode potential is applied to the anode of tube 1 through aprimary coil 4l, the latter being coupled with the secondary coil 5 of aradio transformer'll. 'llhe coil 5 is connected in the'input circuitot asecond tetrode 6, also of the screen, grid type, by utilizing anindirectly Yheated cathode 7. The coil 5 is tuned by a'variablecondenser 6, the rotors of the condensers 3 and 8 being operatedr by acommonl uni-control mechanism 9, shown in dotted lines.

The heater iilament 10 of the tube 6 receives power from a source ofalternating current energy (not shown), it being noted that this sourcecan be the same source which supplies power to the cathode oil tube 11'llhe screen element 11 oi? tube 6 has connected in series therewith atickler inductance coil l2, inductively coupled with the coil 5, oneterminal of the coil 12 being adjustably connected by a lead 13 to aresistor R1, the latter being preferably art of a potentiometer'mechanism general y denoted by the letter P, the latter being preferablyconnected across the terminals of any well known type of power ilter(not shown). The tickler coil 12 is preferably made adjustable so as tovary the degree of regeneration employed.`

rllhe anode 1l of the tube 6 is directly connected by a lead 15 to thecontrol electrode 16 of a pentode tube 17. 'llhe pentode tube 17 alsoincludesv a cathode 18 heated from a is adjustably connected by a lead22 to a resistor portion R5 included in the potentiometer l. A spacecharge electrode 23 is disposed between the screen element 2l and theanode in a manner well known to those skilled in the art, and isconnected 'to the cathode 18. rl`he output circuit of the pentode 17 isadapted for connection to any well known type of utilization means suchas a loud speaker, head phones land the like.

The lead 15 is tapped by a lead 24, and adjustably connected to theresistor R1, the lead 2l including a highA resistance R1, the adjustablecontact of the lead 24 being connected to a point, on the resistor R1,of more positive potential than the adjustable contact point of theleadl 19. rllhe tiometer P further-includes a resistor a resistor R3,bothgconnected iniseries with each other, and in series with .theresistors R1, R1, and R5, the latter three resistors also beingconnectedl in series.- 'llhe cathode 7 of tetrode 6 is connected, byymeans of a lead 24, toY one terminal of the resistor R1, the lead 21including inl series with the cathode, a resistor R1.

'lhe cathode 7- is also connected to an adjustable contact arm 25, bymeans of a lead 26, the latter including a capacity C in series betweenthel cathode and contact arm 25. llt will be noted that the controlelectrode of tetrode 6 is -negatively biased by adjustably 'connectingit to resistor R1 by means of a lead 27, the lead including theinductance coil 5 in series with the control electrode. As statedheretofore, the screen element 11 of the tetrode 6 is ad-justablyconnected to the resistor R1, by means of a lead 13. e

Asan ex lanation of how the direct coupled. ampli er operates, referencewill Ilow e made to the elements specifically shown in the drawing. lheresistor R1 cooperates with the resistor R1 to develop initial grid biasfor the tetrode 6, and to automatically vary the bias for what may betermed drift correction or stabilization. lt is, also, to be noted thatthe lead 27 is adjust'ably connected to the resistor R1, in order to.insure a proper initial negative bias on the control electrode. v

For example if the resistor R7 develops a negative potential of about 16volts with vrespect to the control electrode of the tetrode 6, this willbe opposed by a positive potential oten-l 2 and p.

andR5 divide the anode voltage of pentode` tube 17 into two portions,with the junction at the point 30 where the lead 24, which contains thehigh resistance R6, is connected on the resistance R4, thus giving asuiiicient voltage drop between point 30 and point 31.

The latter point 31 is the pointon the resistance R4 to which the lead19 is connected from the cathode connection on the electrical mid-pointof inductance 20. This insures a drop of about 50 volts,while'incre-asing the current drain on the power filter b Aa neg#ligible amount. The `leads 24 an 19 are adjustably connected to theresistor R4, in orderto insure securing proper negative bias on thecontrol electrode 16 of the pentode 17.

.Tlie high resistance R6 between the output circuit of tetrode 6 and theinput'circuit of the pentode 17 results in a very high amplificatlongain, and it is because this resistance is so high that it isnecessaryto connect the lead 24 to a point 30 on the resistor Rqwhich isa point of more positive potential than the point 31 to which thecathode is connected. The resistor Rs is employed to aid in securing aproper voltage difference between the cathode 7 0f the tetrode c and thecathode 1e of the pentode 17.

Hum in the amplifier, this hum arising most readily in the tetrode 6which acts as a detector as well as an implifier,`is minimized by-meansof the series connection consisting of the capacity C and the adjustableresistance 25, R2, the contact arm 25 being adjusted to the criticalpoint which will result in a point of minimum hum. It will beobviousthat the resistor R2 will take care of a great deal of the hum apparentin the detector output of even a poorly filtered receiver. l y

To illustrate the values of the resistors'employed,-it is noted hereinthat the resistor R7 may have a value of 50,000 ohms; the resistor R1 avalue of 425 ohms; the resistor R2 a value of 200,0hms; the resistor Rsa value of 775 ohms; the resistor R4 a value of 29,700 ohms; `'theresistor R, a value of tion of the tickler coil 12 in series with thescreen 11 of the tube 6. This connection still further increases thesensitivity of the receiver, thus permittin the use of only two tubes,yone a tetrode, an the other a pentode,

it being readily apparent that since the tetrode 6 also operates asadetector stage, the antenna circuit could be cou led directly to thetuned input circuit of t e tetrode 6 and a fairly sensitive receiverstill had.

However, with the addition of a stage of tuned'radio fre uencyamplification employing a screen gri tube ahead of the tetrode 6,

an excellent, and vet inexpensive, receiving circuit is produced.Thiscircuit, it will be further observed, lends itselfreadily toregeneration connection in the detector-amplifier stage employing thetetrode 6,where the anode circuit includes a resistance which-'is sohigh that there is not enough anode current to automatically produceregeneration satisfactorily; the utilization of a tetrode of the screengrid type, it being readily apparent, successfully maintaining feed-backthrough the inter-electrode capacities of the tube at a safe minimumvalue.

While I have indicated and described one arrangement for carrying myinvention into effect, it'will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationshown `and described, but that many modifications may be made Withoutdeparting from the scope of my invention as Set forth in the appendedclaims.

What I claim is:

1. A radio receiving circuit comprising means for collecting signalenergy, means for detecting the collected signals including an electrondischarge tube provided with a screen electrode and having a tuned inputcircuit, a pentode tube having its control electrode directly connectedto the anode of the detecting tube, and means for feeding back energyfrom the screen circuit of the detaching tube to its tuned inputcircuit.

2. In combination, in a receiving circuit a combined detector andamplifier consisting of )a tetrode having a screen electrode and a tunedinput circuit, a pentode output tube having its control `electrodedirectly connected to the anode of the tetrode, and means for feedingback energy from the screen circuit of the tetrode to its tuned inputcir- 100,000 ohms; and the resistor R6 a value of rcuit.

500,000 ohms. It is to be clearly understood that these values are givenmerely for the purpose of illustration, and can be varied in anydesirable manner to l'secure high gain without distortion.

The use of the pentode tube 17 results in a very great increase in .theamplification, and is about equal to adding another stage o'audioamplification. The operation of the receiver is greatly improved by theutiliza- 3. In combination, an antenna circuit, a stage of tuned radiofrequency amplification including an electron discharge tube cou ledthereto, an electron discharge tube provlded with a tuned input circuitcoupled to the first stage,the second tube including a screen element, athird electron discharge tube having its control electrode directlyconnected to the anode of the second tube, means for regenerativelyconnecting the screen element of 4ment of the second tube and thecontrol electrode of the third tube both deriving potential from saidcommon potentiometer.

4. lln combination, in a receiving circuit, a

regenerative screen grid detector, and a pentode output tube having itscontrol electrode directly connected to the anode of the detector,apotential supply potentiometer, all the circuits of said detector andoutput tube being connected to the potentiometer, and means adjustablyconnecting the detector screen grid to the potentiometer.

5. A radio receiving circuit comprising a screen grid tube having atuned input circuit, an `audio frequency amplifier connected in theanode circuit of said tube, and an inductive reactance in the screenelement circuit of said tube coupled in regenerative phase to said inputcircuit.

6; A radio receiving circuit comprising a screen grid tube having atuned input circuit,

- an audio frequency amplifier connected in the screen grid disposedanode circuit of said tube, and mutual impedance between the screenelement circuit and the tuned input circuit of said tube, a

potential supply potentiometer, the' elec- `I trodes of said tube andampliiier being connected to the potentiometer, and means tor adjustablyconnectingl the screen element to the latter.

7. ln combination, a source ot radio irequency energy, a screen gridtube provided with a tunable input circuit coupled to said source, apower am liier tube including a tween the cathode and anode thereof landa shield electrode, at cathode potential, between the screen and anode,a source of energizing current common to the circuits of said tubes,means for directly connecting the anode of said iirst tube to thecontrol electrode of the amplier tube, and means including a highresistance, connecting said anode and control electrode to saidenergizing current source.

8. ln a. radio receiver, a detector stage including a screen gridl tubeprovided with a tunable input circuit, an amplier tube, a

source of energizing current tor the circuits oi said tubes, meansconductively coupling the anode of said detector tube and the controlgrid ot the amplier tube, additional means', including a high impedance,connecting said conductive coupling to said source, and means in thescreen circuit et said detector tube to secure regeneration.,

'9. lin aradio receiver, a detector stage including a screen grid tubeprovided. with a tunable input circuit, a power pentode amplilier tube,a source ci energizing current tor the circuits ot said tubes, meansconductive y coupling the anodevoi3 saidv detector tube andotentiometer.

nordsee the control gird of the amplifier tube, additional means,including a high impedance, connecting said conductive coupling to saidsource, and means in the screen circuit of said detector tube to secureregeneration.

10. lin a radio receiver, a detector stage including a screen grid tubeprovided with a tunable input circuit, an amplifier tube, a source ofenergizing current for the circuits of said tubes, means conductivelycoupling the anode of said detector tube and the control grid o theamplifier tube, additional means including an impedance, so highthatthere is insuclent anode' current in the detector stage to produceregeneration satisfactorily, connecting said conductive coupling to saidsource, and means in the screen circuit of said detector tube to secureregeneration l1. ln a radio receiver, a detector stage including ascreen grid tube provided with a tunable input circuit, an amplifiertube, a source of energizing current for the circuits oi said tubes,means conductively coupling the anode of said detector tube and thecontrol grid of the amplifier tube, additional means, including a highimpedance, connecting said conductive coupling to said source, and meansin the screen circuit of said detector tube to secure regeneration and astage of tuned radio frequency amplification including a screen gridtube coupled to said detector input circuit.

l2. An electric circuit comprising an elecl aving an impedance so highthat there is not enough anode current to produce regenerationsatisfactorily, and means associated with said screen grid circuit forfeeding energy to said 'input circuit in regenerative hase with theenergy transmitted troml said input circuit to said output circuit.

13. lin combination with a potential supply potentiometer, a screen gridtube having a tunable input circuit, connections between the electrodesof the tube and the potentiometer to establish said electrodes atdesired potentials, a source of signal energy coupled to the said inputcircuit, a pentode amplifier tube, means tor directly connecting thecontrol grid of the pentode tube to the anode of the screen grid tube,connections between the electrodes oi the pentode tube and the potenllttiometer to a the pentode electrodes at de-vr potentiomet/er beingadtiometer to fix the pentode electrodes at 'desired potentials, theconnection between the potentiometer and said anode and control gridincluding a high impedance, means for.

regeneratively coupling the screen grid and input circuits of said firsttube, and the connection between the screen grid of said first tube andsaid potentiometer being adjustable. `15. In combination, a source ofradio frequency energy, a screen grid detector tube providedwith atunable input circuit coupled to said source, a ower amplifier tubeincludbeing connected to said otentiometer, the screen grid ofthe firsttubb being connected to a oint on said potentiometer which is negativewith respect to the point on the potentiometer to whichv said power tubecathode is connected.

18. In combination, a source of radio frequency` energy, a screen grid'detector tube provided with a tunable input circuit. coupled v to saidsource, a power amplifier tube including ascreen grid disposed betweenthe cathode and anode thereof and a shield electrode, at cathodepotential, between the screen and anode, a source of energizing currentcommon to the circuits of said tubes, means for directly connecting theanode of said first tube to the control electrode of the amplifier tube,and means including a high resistance connecting said anode and controlelectrode to said energizing current source, and a screen grid radiofrequency amplifier (provided with a tunable input circuit disposebetween said source and detector input circuit.

VALTER VAN B. ROBERTS.

ing a screen gri disposed betweenthe cath- 'I ode and anode thereof anda shield electrode, at cathode potential, between tliescreen and anode,a source of energizing current common to the circuits of said tubes,means for directly connecting the anode of said first tube to thecontrol electrode of the amplifier tube,

, and means including a high resistance, con- A necting said anode andcontrol electrode said energizing currentxsource.

16. In combination, a source of radio frequency energy, a screengridtube rovided with a tunable input circuit couple to said source, apower 'amplifier tube including a screen grid disposed between thecathode and anode thereof and a shield electrode, at cathode potential,between the screen andanode, a source of energizing current including apotentiometer common to the circuits of said tubes," means fordirectlyconnecting the anode of said first tube to the control electrode of theamplifier tube, and means includin a high resistance, connecting saidanode an control electrode to said energizing current source.

17. In combination,I a source of radio frequency energy, a screen gridtube provided with a tunable input circuit coupled to said source, apower amplifier tube including a scr'een grid disposed between thecathode and anode thereof and a shield electrode, at c athf odepotential, between the screen and anode,

a source of energizing current common to the circuits of said tubes,means for directly connecting the anode of said first tube to the con-`trol electrode of the amplifier tube, and means including a highresistance, connecting said anode and control electrode to saidenergizing current source, said source including a potentiometer, thecathode of the said power tube Dt LA@ M R 1,910,500.Walter Van B.Roberts, Princeton, N. el. Remo Rmcmvm@ Gmcmm Patent dated May 23, 1933.Disclaimer filed September 25, ic35,`by theI assignee, RadioCorpora/tion of America. l i

Hereby enters this disclaimer to that part of the claims in thespecification oi sald Letters ,Patent which 1s 1n the following words,to wit:

6. ln comblnation, an antenna circuit, a stage of tuned radio frequencamplification includin an electron discharge tube coupled thereto, an'electron 'charge tube .rovide'd with a tunedinput circuit coupled to therst stage, the second tube inclu lng a screen element, a third electrondischarge tube having its control electrode directly connected to theanode of the second tube, means for regeneratively connecting the screenelement of the second tube to its tuned input circuit, a common sourceof potential for the second and third tubes, a common potentiometerconnected across said source, the screen element of the second' tube andthe control electrode of the third tube both deriving potential fromsaid common potentiometer.

' 8. A radio receivingcircuit comprising a screen g 'd tube having atuned input circuit, an audio frequency ampliier connected in the anodecircuit of said tube, and an inductive reactance in the screen elementcircuit of said tube coupled in regenerative phase to said inputcircuit.

, 10. ln combination, a source of radio frequency energy, a screen gridtube provided with a tunable input circuit coupled to said source, apower amplifier tube including a screen grid dlsposed between thecathode and anode thereof and a shield electrode, at cathode potential,between the screen and anode, a source ci ener is` current common to thecircuits of said tubes, means for directly connecting the'anodc of saidfirst tube to the control electrode of the am liier tube, and meansinclu it y: a high resistance, connecting said anode and control eectrode to said energizing current source. 12. ln a radio receiver, adetector stage including a screen grid tube provided with a tunableinput circuit, a power pentode amplifier tube, a source of energ currentfor the circuits of said tubes, means conductively coupling the anode ofsaid detector tube and the control grid of the amplifier tube,additional means, including a high impedance, connecting said conductivecoupling to said source, and means in the screen circuit of saiddetector tube to secure regeneration.

{Oieelal Gazette October 15, 1.935.]

f oleoummem i 1,910,500.-Waer Van B. Roberts, Princeton, IN. J. RamoRncm'vmc Cmcul'r. l

Patent dated May 23, 1933. Disclaimer -iled November -14,- 1935, by theassign Radio Corporation of America.' The disclaimer ed on September 25,1935,was in error in that the language of said claims was not correctlyrecited;-

j-That it was the mtentlon ofthe undersigned assignee to disclaim'thesubject matter of claims 6, 8, 10 and 12 of said Letters Patent andnotthe language of the Y claims recited; in the disclaimer filedSeptember/.25, 1935;

That said error arose through inadvertance, accident, or mistake andwithout any fraudulent or decetive intention. l v Your Petitioner, terefore, hereby retracts that portlon .of the disclaimer filed September25, 1935,which purported to recite the language of claims 6, 8, 10, and12 and hereby enters `this disclaimer to that part of ths'claims in thespecification of said Letters Patent which is in the following words,'to wit:

' 4screen element to the' latter.

6. A radio receiving circuit comprising a screen grid tube having latuned input circuit an audio fre uency amplifier connected inthe anodecircuit o f said tube, and

mutual impedance et veen the screen element circuit and the tuned inputcircuit' of saidtube, a potential supply potentiometer, the electrodesofsaid tube and ampli-.

ier'being connected to the potentiometer, and means for 'adjustablyconnecting the u8. In a: radio receiver, a detector stae including ascreen grid tube provided l ,with la. tunabile'input circuit, anamplifier t e, a source'- of energlzm current for the circuits of saidtubes, means conductively couplingthe anode of sa1d detectortube and thecontrolgrid of the amplifier tube, additional'means, includinga h' himpedance connectin said conductive coupling to said source, and meansin t e screen circuit of said etector tube to secure regenerationl' '10.Inra radio receiver, a detector stage mcludng a screen gridtube/provided lwith a tunable input circuit, an amplifier tube, a sourceof ene 'zxn current for the cirsai cuitsof said tubesmeans conductivelycoupling the-jauode o detector tube and the Acontrol gridfof theamplifier tube, additional means including an impedance, so

n' high that theli'e is uiicient anode current in the detector sta e toproduce regeneration satisfactorily, connecting said conductive couplingtoY sai source, and means 1n the screen cincuit of said detector tube tosecure regeneration.

5 12. electric circuit comprising an electr emission cathode, an anode,a control grid, and a screen grid, a tunable input circuit connectedbetween said cathode and said control g'rid, an output clrcult connectedbetween said cathode and said anode, a source of `energlzi'ng currentfor the anode,

control id and screen grid circuits of said tube,l said' output circuithaving an impedance so ighf' that there is not enough anode current toproduce regeneration satisactorily, and means associated with saidscreen gridjcircult for feeding energy to sa1d input clrcuit inregenerative phase with the energy trans' 'tted from said input ycircuitto said cut ut circuit. [Qfc' Gazette December 3,19351 on discharge tubehaving an

